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DIPOL Weekly Review - TV and SAT TV, CCTV, WLAN

No. 31/2007 (Sept 17, 2007)

802.11n - the future of WLAN? Many analysts think that full ratification of the 802.11n standard will be the next strong impulse to growth of wireless market. Unfortunately, the standard meant for such applications like transmission of home multimedia at the speed up to 250 Mbps is still far from final acceptance (anticipated by the end of 2008, or even later). But the approval of the set of agreements called Draft 2.00 (in January 2007) moved the increasingly popular wireless networking technology a step further. Manufacturers and customers have been given reassurance that amendments to the final standard won't be essential, and the Draft 2.0 gear will cooperate with that compliant to the final version. In August 2007 Wi-Fi Alliance certified the first group of 71 devices compliant with Draft 2.0. Among them there is the gear for Apple TV.The list of certified devices

Quick implementation of 802.11n has been announced by TP-link

Antennas at the end of the world - where are they? The old Celtic magical path, going to periphery of the world, for above a thousand years gathered pilgrims from whole Europe. Primarily, the aim was Finister Peninsula, the most westward point of the continent. In the Middle Ages the purpose changed and the number of people on the path increased, the cult of Saint Jacob attracted pilgrims from all over Europe to undertake a few month's or even a few years' expeditions. Roads beginning in Germany, France, Italy and even in British Isles, for a few hundreds years represented communication core of Europe, the place of information exchange and deep reflection on life. What is the name of the peninsula with these antennas? - the answer is at the end of this issue.Report from the path to the End of the World

Antennas at the end of the world - where are they?

Can one save on connectors in antenna installation? Connectors are the part of transmission path which do not have significant impact on the cost of an installation, but are crucial to signal quality, labor intensity, and reliability of the system. Every connector, even of top quality, causes additional loss of signal, so the number of connections should be limited to real needs. It is important to use high-quality connectors. The important parameter is voltage standing wave ratio (VSWR), indicating how much of the power of the signal is reflected back to the source of signal. In the case of satellite IF the parameter should not exceed 1.5, which means that ca. 4% of the signal's power comes back to the source. Another way of describing transmission parameters is giving the value of return loss, i.e. the ratio of the amplitude of the incident signal to that of the reflected one. This parameter, described in dB, should be as large as possible. For example, 20 dB means that the reflected signal has 10 times lower amplitude than that of the input signal. Screening efficiency describes suppression capability of the connector as regards external interferences. This parameter is also given in dB - for brand-name connectors its value is about 70 dB. The connectors used outdoors have to be protected against penetration of water. It is so important because even a drop of water would increase VSWR even by several tens of percent, changing energy of the signal into heat. In professional applications there are usually used crimped connectors, much quicker to mount and much more reliable. Professional installers know that often most of the time is spent on making connections and checking them.Professional crimped connectors for TRISET-113 and Triset-11 cables

Which multiswitch is suitable for one-family home? Due to high quality and flexibility (possibility of further development of the installation) we recommend for that purpose the multiswitches MS-952/951 R70952, R70951. The user may start the installation with MS-952 R70952 allowing distribution of four complete sets of FM/TV/SAT signals. When the family or house grows, use of additional MS-951 module will enable the family to get next four complete signals. Building multiswitch installations it is also worth to remember that the new "Twin" receivers (two-in-one receivers with HDD) require two independent signals. The multiswitches MS-952/951 are equipped with passive terrestrial TV path. Such solution requires to ensure adequate levels of the signal (using amplifiers in terrestrial installation), but does not cause possible complications with overdriving the multiswitches. The devices cooperate with satellite receivers supporting Tone Burst (e.g. in Poland - those distributed by Cyfra+ platform).Multiswitch installation with optional connection of CCTV camera

Camera housings with concealed cables. This kind of housing gains popularity due to its merits. Both the signal and power cable is hidden inside the bracket. The camera is better protected against malicious damaging and looks better. Such housings are available in 12V and 230V versions, equipped with heaters, for competitive prices.Housings and brackets with concealed cable/s

Modern housings - concealed cables

Traditional housing - there is a risk of damaging the cable

CCTV system with megapixel cameras - monitoring of cash desks. These places, crucial for every business, are predisposed to thorough monitoring, both due to safety requirements of the post and often the needs for additional documentation of transactions. It is very important there to ensure distinction of details, despite usually quite wide field of observation. These criteria are not attainable with analog CCTV cameras, offering up to 720 x 576 pixels. The problem can be solved by application of compact IP cameras PiXORD P405M K1135 with 1.3 Mpix resolution and MPEG-4 compression, which provide perfect images of 1028 x 1024 pixels. The images can be digitally enlarged two times still ensuring the accuracy of best analog images without processing. Another advantage of these cameras is cheap installation (cabling) and flexibility of the system (development in the future), thanks to operation within local computer network (LAN). Each camera is equipped with NVR utility program allowing recording of images even from 32 cameras (continuous or triggered by motion detection). It allows to monitor up to 32 cash register desks within one monitoring system. All cameras are connected via switches too the computer with NVR installed.

AI lens - how is it built and how does it work? - Part 2. Last week we outlined the principle of iris control, this time we examine the electromagnetic actuator that drives the blades. How to build such a driving system that would have linear characteristics (position as the function of the control voltage)? It is not an easy task, especially in so tiny device as the lens is. The secret lies in the construction of the electromagnet, and special system of position control. The device is built with external jacket (the stator) being a permanent magnet, and the movable element (say the rotor, but its angle of rotation is limited to 90 degrees only).

This arrangement of magnets is immersed in the magnetic field generated by set of two coils - "Drive" and "Damp". Drive coil resistance is about 200 ohm, and it is the main winding of the electromagnetic actuator. The current that flows through the winding changes direction of magnetic field to the opposite, so the rotor changes its position by 90 degrees. Such an actuator allows 2 states: fully opened or closed iris. How to get intermediate angles? For that purpose there is used feedback control system with the braking "Damp" winding.

The winding has larger number of turns, so its resistance is usually between 500-1000 ohm. The "Damp" coil works as inductive sensor of movement (in the close-loop control system driving the "Drive" winding). This construction is quite simple and effective (together with the dedicated control system) and does not raise essentially the cost of the lens.

Construction of the actuator driving iris blades in AI lens

In a week - we will have closer look into the control system of the actuator.

Compact camera with adjustable focal length. Compact cameras are ready to work just after unpacking and easy to mount. They can be installed outdoors, due to hermetic housings with built-in heaters and IR illuminators. The only limitation was fixed viewing angle, because any interference of the user (change of the original lens) was not allowed (risk of loss of hermetic qualities and the manufacturer's warranty). But the situation has changed recently - there are available now compact cameras with lenses allowing change of viewing field. The example is the camera VF-817 M11277, with adjustable focal length from 4 to 9 mm.

PoE adapter with leads for LANs. The PoE set N9205 contains two passive devices shown in the picture. They are equipped with RJ-45 and 2.1/5.5mm (power) connectors, and prepared for work with majority of popular WLAN devices (TP-Link, Planex GW-AP54SP-P, Linksys WRT54GL, CC&C WA-2204C oraz WA-2204A), as well as other IP devices, like PIXORD.

We have tested cooperation of the PoE adapter with 1.3 Mpix IP camera PIXORD P405M K1135, using the original AC/DC adapter (output: 5V/1A) included in the camera set. We also used 10 m of FTP cable, terminated with RJ-45 connectors. The cable had no negative impact on the operation of the camera or the quality of transmitted image and sound.

Problems with implementation of LAN? - Let's build WLAN. Internet access is nowadays indispensable functionality of every office block, hotel or warehouse. When the building is not equipped with wired LAN infrastructure, the quick, cheap and effective way of solving the problem is wireless network. The diagram shows an example of developed office network based exclusively on wireless solutions. The router is linked directly to an xDSL modem or node of local network (with lRJ-45 connector).Recommended devices:

the router TL-WR542G N2950 and Access Point TL-WA501G N2940 configured as Repeater - for improving link quality in the further part of the story,

WLAN antennas in buildings. The deployment of access points and antennas in buildings should be the result of practical tests. Usually we situate AP in the place as near as possible to the central point of the building. The necessity of covering the whole space of the building is the reason that only omnidirectional antennas can be used . Such characteristics is typical for stub antennas (usually included in the set) directly mounted to the APs. Very often, when the building is large and the antenna/s is not capable of covering the whole area, the users try to employ antennas with higher gain. The results may be unsatisfactory, because higher gain of the antenna means more directional characteristics, so uneven coverage of the area (improvement in some directions and deterioration in the others). That's the reason why in general only omnidirectional antennas should be used. Such antennas can usually provide WLAN on one floor. Having good signal on the floor, we may have problems on other floors. The best solution seems to be placing AP on each floor, ensuring adequate separation distances between the APs. For 2.4 GHz band there may be recommended the antenna A72531 (8 dB), for 5 GHz - MA-WO58-9X A73121 (9 dB). Both antennas use vertical polarization.WLAN antennas

Example deployment of APs in large office block with reinforced concrete ceilings and the optimal shapes of antennas' characteristics

Finister Peninsula (finis terra - the end of the world) - Spain. The extension of the route to Santiago Compostella - the end of the world for medieval people. Antenna of shortwave radio station at the end of the peninsula, the most westward antenna in Europe.

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